1. Field of the Invention
The present invention relates to a narrowband module inspection device for inspecting the narrowband efficiency, wavelength selection characteristics, and other narrowband performance of a narrowband module.
2. Description of the Related Art
Attention is focusing on the use of excimer lasers as light sources in steppers used in the fabrication of semiconductor devices. This is because numerous outstanding advantages can be expected. These include the capability to extend the lithography limit to 0.35 .mu.m and lower as a result of the short wavelengths of an excimer laser; deeper depth of focus than previously-used mercury lamp g-line and i-line peaks at the same resolution; a large exposure area can be achieved with a small numerical aperture (NA) lens; and high power levels.
However, when this excimer laser is utilized as the light source in a semiconductor exposure system, synthetic quartz is the only lens material capable of being fabricated into an optical system for excimer laser wavelengths (the wavelength of a KrF excimer laser is 248 nm, and that of an argon excimer laser is 193 nm); but a synthetic quartz material alone cannot be furnished with a chromatic aberration function.
For example, in the case of spontaneously emitted energy of a KrF excimer laser, the spectral line width is a wide 300 pm, and left as-is, the chromatic aberration of the exposure system lens cannot be ignored, and resolution sufficient for exposure results cannot be achieved.
Accordingly, when utilizing an excimer laser as the light source of a semiconductor exposure system, the bandwidth of the laser light is narrowed by providing inside the laser resonator a narrowband module, comprising a wavelength selection device, such as an etalon, or grating and prism.
When inspecting the performance of a narrowband module such as this, in the past, the narrowband module was mounted into an actual laser, the actual laser light emitted from the laser chamber was incident on the narrowband module, and the outputted light thereof was inspected.
Consequently, with prior art, there are problems such as
(1) an actual laser system is required to confirm the performance of a narrowband module; PA1 (2) it takes time to inspect and adjust a narrowband module; and PA1 (3) when the desired performance is not exhibited in the laser output light, it is impossible to specify whether the cause thereof is a malfunction in the narrowband module, a malfunction in another component element, such as the laser chamber, monitor module, or the like, or a discrepancy in the optical axis adjustment of the resonator.
Further, a technology for inspecting the optical characteristics of a diffraction grating used in an optical disc device and the like is disclosed in Japanese Patent Laid-open No. 2-129844. That is, with this prior art, a single-wavelength collimated beam is incident on a diffraction grating, the positional shift between the light-intercepting position of the first-order light from the diffraction grating and a reference light-intercepting position is measured, and the pitch positional shift of the diffraction grating is inspected on the basis of this measured light-intercepting positional shift. Further, with this prior art, a single-wavelength collimated beam is incident on a diffraction grating, the quantity of light of the first-order light from the diffraction grating, and the quantity of light of a zero-order light are measured, and the groove depth of the diffraction grating is inspected based on a comparison of these light quantities.
As for this prior art, although an inspection related to the physical shape of a diffraction grating in an optical disc device can certainly be performed for a diffraction grating unit, this prior art only detects the physical shape of a diffraction grating utilized in an optical disc device and the like, but does not directly detect the bandwidth-narrowing performance of a diffraction grating.
That is, in the field of lasers, such as an excimer laser, there is a need for an inspection device capable of directly inspecting and adjusting, as a narrowband module unit, a variety of narrowband performance, such as the intensity distribution, spectral line width, center wavelength, narrowband efficiency, and wave front shape of the band-narrowed light beam generated from a narrowband module.